AP Chemistry Wk5

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AP Chemistry Wk5

• Christopher Chui

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Representing Chemical Changes

• Chemical equations are used to represent chemical
  changes
• Reactants are the starting substances and
  products are the substances formed in chemical
  reactions
• The symbol (aq) indicates a water solution of a
  substance (g) a gas (l) a liquid (cr) a solid

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Balancing Equations

• 1) Determine the reactants and the products
• 2) Assemble the parts of the chemical equation
• 3) Balance the equation
• Balanced equations have the same kind and numbers
  of atoms on each side
• Coefficients, not subscripts, may be changed to
  balance an equation
• Never change a subscript to balance an equation

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Classifying Chemical Changes

• Single Displacement element compound ? element
  compound
• Double Displacement compound compound ?
  compound compound
• Decomposition compound ? two or more elements or
  compound
• Synthesis element or compound element or
  compound ? compound
• Combustion hydrocarbon oxygen ? carbon dioxide
  water

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Mass-mass Relationships

• Step 1 Write the balanced equation
• Step 2 Find the number of moles of given
  substances and required substance
• Step 3 Convert the grams of given substance to
  moles
• Step 4 Determine the mole ratio from the balance
  equation
• Step 5 Express the moles of required substance
  in terms of grams

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Stoichiometry the quantitative study of chemical
reactions

• Percentage yield is a comparison of the actual
  amount of product with the theoretical amount of
  product
• If the energy is absorbed in a reaction, the
  reaction is endothermic
• If energy is released in a reaction, the reaction
  is exothermic
• Chemical changes are accompanied by a change in
  energy
• The minimum amount of energy required to start a
  reaction is the activation energy for that
  reaction